Manufacture of tetraethyllead



United States Patent MANUFACTURE OF TETRAETHYLLEAD Harold J. Madden, Baton Rouge, La., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application August 16, 1950, Serial No. 179,885

6 Claims. (Cl. 260-43 This invention relates to an improved method of making tetraethyllead.

Tetraethyllead is an important commercial product because of its extensive use as an antiknock agent. The present commercial process for its manufacture comprises first forming solid particles of a sodium-lead alloy and then reacting the lead alloy particles with ethyl chloride at temperatures above 70 C. according to the following equation The sodium-lead alloy is made by first melting a mixture containing the proper proportions of sodium and lead, solidifying the melt and then breaking and grinding the solid melt into particles suitable for use in the reaction with ethyl chloride. The solidifying and grinding operations are expensive especially when considering that not only must fresh quantities of lead be alloyed in this manner but the three parts of free lead formed in the reaction, according to the above equation, must be realloyed. Furthermore the mere handling of large quantities of solid alloy is cumbersome and expensive. Also the rate of reaction between alloy thus formed with ethyl chloride is not as high as desirable, particularly in a continuous process where reaction rate is of prime importance.

It is therefore, an object of my invention to provide an improved reaction between ethyl chloride and a sodiumlead alloy made and used in an unusual and difierent form, thereby eliminating many of the above disadvantages of the present process.

I accomplish the above object by introducing molten alloy directly into ethyl chloride. Due to the inherent thermal instability of tetraethyllead at temperatures much above 100 C., and the volatility and thermal stability characteristics of ethyl chloride, it is surprising and entirely unexpected that molten alloy at temperatures of 375 C. and higher could be charged into a body of liquid ethyl chloride with no explosive hazard and with a reaction proceeding smoothly and at a rate faster than that obtained from alloy used in the present commercial process.

The unexpected advantage of the fast reaction rate thus obtained is important to the tetraethyllead process in that higher capacities are obtained, thereby substantially reducing equipment costs. This is particularly true in a continuous process where reaction rate is frequently the difference between a profitable operation and an unprofitable one. Furthermore, while the ultimate percentage yield in a batch operation is not substantially affected, the practical ultimate yield in a continuous operation is affected. For example, the highest yield of tetraethyllead based on the weight of lead charged, when ground alloy was fed continuously to a body of ethyl chloride at the maximum feasible residence time, was only about per cent whereas above per cent can be readily obtained when molten alloy is employed. Thus ice within practical limits the ultimate yield is substantially improved by a faster reaction rate.

Another advantage of my process particularly applicable to a continuous or semi-continuous process is the ease of passing molten alloy across a pressure differential such as introducing alloy into a reaction zone under pressure. Such an operation is difficult with a solid alloy.

Besides the above advantages, molten alloy versus solid alloy has the following advantages; easier to handle, less expensive alloying operation following the melting step, less complicated equipment used in the reaction zone, less factory space required for the alloy plant, and heat savings etiected because alloy is not cooled to room temperature and re-heated for reaction.

In one broad embodiment, the operation of my invention is conducted as follows: sodium and lead in the proper proportions, preferably that corresponding to NaPb although alloys of other proportions will exhibit the same effect, such as NazPb and NasPb i, are heated to a temperature suificient to melt the mixture, which temperature is about 375 C. for NaPb. The molten alloy is then sprayed or extruded continuously into a body of ethyl chloride and the reaction allowed to proceed at a temperature between 40 C. and 100 C. The reaction products are subsequently separated in the usual manner. The ethyl chloride in the reaction zone is prefe'rably in excess of the amount required in the equation given above, the preferable ratio of ethyl chloride to lead being between about 0.5 to l and 6.25 to 1 by weight. The pressure used should be suflicient to maintain the ethyl chloride in the liquid phase at the reaction temperature employed. The residence time is not critical, but for practical purposes should be within 3 minutes and 30 minutes.

The molten alloy particle size, while not critical is important, and for best results should be maintained below i 4 mesh, preferably between 8 mesh and 300 mesh.

Within the above scope of my invention the method of introducing the molten alloy into the reaction zone containing the ethyl chloride is unimportant. Some of the ways that introduction of the molten alloy can be accomplished are: spraying through a suitable atomizing or spray nozzle; extruding continuously or dropwise through an orifice or multiple orifices; and dropping onto a spinning disc. Good results are also obtained if the molten alloy is first introduced into cold liquid ethyl chloride and the mixture then heated to the reaction temperature.

My invention can be further understood by referring to the following working examples in which the parts are by weight and the yields are by weight based on the amount of lead charged.

Example I To a reaction vessel, equipped with an agitator, a jacket 7 for circulation of heating and cooling liquids, a reflux condenser, a charging port through which molten material can be charged under pressure, and a discharging port through which the reaction materials are rapidly discharged, are added 100 parts of molten NaPb alloy at a temperature of 400425 C. The alloy is rapidly fed through a inch orifice into 196 parts of ethyl chloride containing 0.2 part of acetone. By circulating a liquid heated to the proper temperature through the autoclave jacket and controlling the reflux from the reflux condenser, the temperature of the reaction mixture was maintained at (3., throughout the reaction period. The reaction is allowed to progress for five minutes with good agitation, then the reaction mass is rapidly discharged through the discharge port into a suitable receiver, which contains a large excess of cold benzene and a vent port through which excess ethyl chloride is vented. The benzene containing the tetraethyllead formed is removed from the solid-reaction products by filtration, and the residual tetracthyllead recovered from the solid by-prQducts by extraction with additional benzene. Recovery of the tetraethyllead from the benzene solution resulted in 30 .3 parts of product, or a yield of 21.6 per cent based on the'lead presentin the sodiumlead alloy.

Toillustrate another mode of operation in which the alloy is first introduced into cold ethyl chloride and sub? sequently reacted, the following example is given:

Example II One hundred parts of molten NaPb alloy at a temperature of 4D042,5 C., is forced by a pressure of nitrogen through a spray nozzle into 196 parts of ethyl chloride maintained at a temperature below 25. C., to give an. alloy with the following particle size distribution: larger than 35 mesh, 8 per cent; 35-80 mesh, 51 per cent; smaller An NaPballoy was prepared in the usual way by melting and mixing together sodium and lead metal in equal molecular proportions, which were then allowed to solidify by slowly cooling to room' temperature. The solid alloy was broken and ground to a particle size of 8-20 mesh. This material was then reacted under the same conditions as for Example I and 11. With a charge of 196 parts ethyl chloride, 0.2 part acetone, and 100 parts of the 820 mesh alloy formed as above, a five-minute reaction gave only 20.7 parts of tetraethyllead, or a yield of only 14.7 per cent based on the lead present in the sodium-lead alloy.

' Example IV An NaPb alloy was prepared by blending 63 parts of 8-20 mesh with 37 parts of 2050 mesh alloy which had in the conventional Way. Such an increase isv significant and exceedingly important commercially.

The above examples are illustrative of my invention and other operations and apparatus can be used within the scope of the following claims.

I claim:

1. In a process of reacting an alloy of lead with ethyl chloride to make tetraethyllead, the improvement comprising introducing a molten sodium-lead alloy into a reaction zone .conti illing a liquid reaction medium consisting essentially of ethyl chloride.

2. A process for making tetraethyllead Whichcomprises introducing a molten sodium-lead alloy'into a body of liquid predominating in ethyl chloride.

3. The process of claim 2 in which the molten alloy is NaPb and is reacted with the ethyl chloride as it is introduced. V V

4. The process of claim 2 in which the liquid predominating in ethyl .chloride also contains by weight about 0.2 part of acetone, per 196 parts of ethyl chloride.

5. The process of claim 2 in whichthe molten alloy is introduced as particles in the size range of 8 to 30 mesh, in a proportion providing for every part of lead from about 0.5 to 6.25 parts of ethyl chloride by weight, and the mixture is subjected to agitation.

6. The process of claim 2 in-which the molten alloy is NaPb introduced as particles in the size rangeof 8 to 300 mesh and in a proportion providing for every part of lead from 0.5 to 6. 25 parts of ethyl chloride by weight,

and the alloy is reacted with the ethyl chloride for from 3 to 30 minutes at a temperature from to C.

References Cited in the file of this patent UNITED STATES PATENTS 1,652,812 Calcott et al Dec. 13, 1927 1,692,926 Caleott et al. Nov. 27, 192.8 1,697,245 Kraus et al. Jan. 1, 1929 1,974,167 Voorhees Sept. 18, 1934 2,091,114 Daudt Aug. 24, 1937 2,310,806 Nourse Feb. 9, 1943 FOREIGN PATENTS 453,271 Great Britain Sept. 1, 1936 

1. IN A PROCESS OF REACTING AN ALLOY OF LEAD WITH ETHYL CHLORIDE TO MAKE TETRAETHYLLEAD, THE IMPROVEMENT COMPRISING INTRODUCING A MOLTEN SODIUM-LEAD ALLOY INTO A REACTION ZONE CONTAINING A LIQUID REACTION MEDIUM CONSISTING ESSENTIALLY OF ETHYL CHLORIDE. 